The regulation of gene expression in mammalian cells is complex. Human fibroblast interferon production in poly(I) poly(C)-induced cultures of diploid human fibroblasts (FS-4 strain) is subject to a post-transcriptional (translational) repressor mechanism which appears to inactivate or degrade interferon mRNA. An inhibition of this repression by appropriate use of inhibitors of RNA (e.g. DRB, 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole) and protein (e.g. cycloheximide) synthesis leads to a marked (approximately 50-fold), paradoxical enhancement of human interferon yields ("superinduction"). Increased interferon mRNA stability in superinduced cells is the major contributor to this phenomenon. We intend to: 1. Develop a cell-free system to investigate the regulation of human fibroblast interferon MRNA stability. This line of work should lead to the eventual biochemical characterization of the molecules involved in the post-transcriptional repressor mechanism. 2. Carry out further investigations of the synthesis, structure and function of human fibroblast interferon mRNA. We will investigate the size of the fibroblast interferon transcription unit, the regulation of its transcription, the role of 3'-terminal poly (A) in the appearance of cytoplasmic interferon mRNA and in its function and determine the structure of the 5' end of interferon mRNA. 3. Develop improved procedures to enhance human fibroblast interferon yields from diploid cell cultures and to evaluate the use of DRB as a superinducing adjuvant in vivo. These investigations not only address fundamental questions in molecular cell biology, but also should provide a basis for obtaining larger amounts of human fibroblast interferon that may be used in the clinic against a variety of viral and neoplastic diseases of man.